Conventional steam turbines employ one of two exhaust orientations. One such orientation places the condenser (to which the exhaust must lead) below the turbine. This requires a large foundation on the order of 40 to 50 feet in height. In this orientation the vacuum load created by the condenser helps anchor the turbine to the foundation, which is particularly helpful in earthquake shock loading situations.
The problems associated with such a large foundation are two fold. First, such a design requires an enormous quantity of steel reinforced concrete and I-beams. Second, the foundation must be very rugged and the more extended it is, the more difficult it becomes to achieve this ruggedness, the necessary specifications being in terms of lateral and transverse vibration dynamics, earthquake response, etc.
The other commonly used orientation eliminates the need for such a tall foundation by placing condensers on either side of the turbine and running the exhaust to both. The reason two condensers are used is that by placing one on either side the vacuum load created by the condensers can be used to balance each other and not displace the turbine from the center line of the shaft.
The problem with this two condenser side exhaust design is the cost of the additional condenser, which is used not so much for its condensing capacity, as it is as a means of balancing the load on the turbine.
In addition, the advent of combined cycle power plants that can use a combination of fossil fuels and nuclear energy for their operation requires an overall structure for supporting the different energy sources. The use of a large foundation in combined cycle power plants is not suitable for use in a combined cycle power plant.